1. Field of the Invention
The present invention relates to a shadow mask for a CRT, and more particularly, to a shadow mask for a CRT which is capable of preventing a curvature of an effective face of a shadow mask installed in a CRT from deforming, and facilitating welding a skirt portion to a frame of the shadow mask.
2. Description of the Background Art
A color CRT is a display instrument widely used for an observation of an oscilloscope or a radar as well as a television receiver.
The color CRT serves to transmit a color image for users"" viewing which is reproduced. A florescent screen consisting of a red, green and blue florescent materials having three primary color light emitting spectrum of light, graphite, that is, an optical absorption substance, and an aluminum film for improving a luminance, are hit by an electronic beam. The electronic beam passes through a shadow mask functioning as an electrode by sections for the electronic beam just before it hits the florescent screen.
FIG. 1 is a sectional view of a general color CRT in accordance with a conventional art. As shown in the drawing, the color CRT adopting the shadow mask includes a panel 1 positioned at the front surface, a funnel 2 adhesively attached to the rear end of the panel 1, forming a vacuum outer casing container.
An electric gun 3 radiating an electron beam 10 is hermetically sealed inside a neck portion 12, that is, the end portion having relatively smaller diameter in the funnel 2. A deflection yoke 8 is mounted at the outer circumferential side of the neck portion 12, to deflect the radiated electron beam to the whole screen.
A florescent screen 4 made of red color (R), green (G) color and blue (B) color is formed on the inner surface of the panel 1, and a shadow mask 5 is positioned spaced apart for a predetermined distance from the florescent screen 4. The shadow mask 5 is supportedly combined by a frame 6 positioned inside thereof.
An inner shield 11 is combined to the inner end portion of the frame 6, preventing the deflected electron beam 10 from being influenced by an external magnetic field.
In the conventional color CRT constructed as described above, the electron beam 10 radiated form the electric gun 3 is deflected to a desired portion of the screen 4 by the vertical and horizontal deflection magnetic field and passes a plurality of through holes (not shown) formed at the shadow mask 5 to hit each florescent screen 4 made of the red color, green color and blue color by sections, thereby displaying an image.
In more detail, three electron beams 10 of red, green and blue color are radiated from the electric gun 3 to implement a color image, the three electron beams 10 respectively pass one through-hole of the shadow mask 5 and hit a corresponding florescent material pixel of the florescent screen 4, thereby displaying a desired color image.
FIGS. 2 and 3 illustrate a form of the shadow mask 5, of which FIG. 2 is a plan view of the shadow mask before being mounted and FIG. 3 is a perspective view of the shadow mask after being mounted.
As shown in the drawings, the shadow mask 5 includes an effective face 13 on which a plurality of through holes for passing the electron beam 10 are formed in a predetermined pattern, and a skirt unit 14, forming an edge of the effective face 13, is bent at the end portion of the effective surface 13 and half-etched. The skirt unit 14 has a predetermined length so as to be welded to the frame 6.
The skirt unit 14 is welded to the frame 6, rendering the shadow mask 5 to maintain a predetermined space with respect to the inner side of the panel 1.
FIG. 4 is a sectional view showing a curvature deformation state When the shadow mask of FIG. 3 is mounted. FIG. 5 is an enlarged sectional view showing the curvature deformation of the effective face occurring when the shadow mask mounted in the color CRT is combined to the frame.
In order to reduce a sinking phenomenon (A) of the effective face 13 occurring as the skirt unit 14 is widened outwardly due to the elasticity of the material of its own as shown in FIG. 4, and in order to prevent the deformation (B) of the curvature where the effective face 13 is moved outwardly as the skirt unit 14 is moved inwardly when the shadow mask 5 is combined to the frame 6 as shown in FIG. 5, a plurality of notches 15 are formed or a plurality of beads 16 are formed in the width direction of the skirt unit 14, to reinforce its strength.
Reference xe2x80x98Sxe2x80x99 denotes a degree of the widening due to the elasticity of the skirt unit 14 itself.
However, as for the shadow mask for the color CRT in the conventional art, the sinking phenomenon (A) and the widening phenomenon (S) by the elasticity of the skirt unit 14 itself are prevented to a degree in the vicinity of the beads 16 by virtue of the plurality of beads 16, but such effect is degraded in the portions between the beads, generating the skirt-widening phenomenon depending the portions.
In addition, such widening phenomenon makes it difficult to position the end portion of the skirt unit and the end portion of the frame to the normal position for welding in assembling the mask to the frame, degrading a working efficiency. And, the deficiency in the assembly causes the deformation to the curvature of the effective face 13 of the shadow mask, degrading the property of the CRT.
Therefore, an object of the present invention is to provide a shadow mask for a color CRT having a reinforcing means successively operable along the outer diameter of a skirt unit of the shadow mask so as to reduce widening of the skirt unit when the mask is mounted as well as preventing curvature of an effective face from deforming.
Another object of the present invention is to provide a shadow mask for a color CRT for which the end portion of its skirt unit and the end portion of a frame are readily positioned at the normal portion in combining the skirt unit and the frame, thereby improving a working efficiency.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described herein, there is provided a shadow mask for a color CRT including: an effective face having a plurality of electron beam through holes and having a predetermined curvature; and a skirt unit extendedly bent at an outer portion of the effective face at a predetermined angle in the axial direction of the CRT, so as to be combined to the frame, the skirt unit of the shadow mask having a plurality of vertical beads in parallel to the axial direction of the CRT and at least one horizontal bead formed in the lengthy direction almost perpendicular to the vertical bead.